Organocobaloximes with mixed dioxime equatorial ligands: a convenient one-pot synthesis. X-ray crystal structures of BnCoIII(dmgH)(dpgH)Py and BnCOIII(chgH)(dpgH)py

Gupta, B. D.; Yamuna, R.; Singh, Veena; Tiwari, Usha; Barclay, Tosha M.; Cordes, Wallace

doi:10.1016/s0022-328x(01)00731-8

Cited by 20 publications

(37 citation statements)

References 26 publications

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“…The benzyl group has been seen to orient over the dpgH group in the recently reported X-ray structure of PhCH 2 Co(dioxime)(dpgH)Py complexes [dioxime = gH, dmgH, chgH] [14]. Keeping this in view, we have also synthesized [PhCH 2 Co(dpgH)(dmgH)] 2 -l-Pz and reported its X-ray structure.…”

Section: Introductionmentioning

confidence: 69%

“…We have recently observed in the X-ray structures of PhCH 2 Co(dioxime)(dpgH)Py complexes [dioxime = gH, dmgH, chgH] that the benzyl group leans towards the dpgH equatorial wing and the phenyl ring of the benzyl group lies above one of the dpgH unit due to p-p interaction [14]. In view of this it would be interesting to study the X-ray structure of a pyrazine bridged benzyl dicobaloxime with mixed dioxime ligand, [PhCH 2 Co-(dmgH)(dpgH)]-l-Pz.…”

Section: X-ray Crystallographic Studies: Description Of Structurementioning

confidence: 99%

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Pyrazine bridged benzyl dicobaloximes: Competition between π-interaction and steric crowding in crystal structure

Mandal¹,

Gupta²

2005

Journal of Organometallic Chemistry

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Section: Introductionmentioning

confidence: 69%

Section: X-ray Crystallographic Studies: Description Of Structurementioning

confidence: 99%

Pyrazine bridged benzyl dicobaloximes: Competition between π-interaction and steric crowding in crystal structure

Mandal¹,

Gupta²

2005

Journal of Organometallic Chemistry

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“…In the absence of crystal structure it was assumed that the bulkiness of two cobaloxime units caused the hindered rotation. Later, the crystal structure of 2-NO 2 -C 6 H 3 -[CH 2 Co(dmgH) 2 Py] 2 showed that the bulkiness was similar to simple benzyl cobaloxime, BnCo(dmgH) 2 Py, and the benzyl group was oriented in such a way that it lay over one of the dioxime wings, as seen earlier in many of the crystal structures of benzyl cobaloximes. , This has posed another question: whether the π-interaction between the benzyl group and the dioxime ring current 6d,7 contributes to the nonequivalence of the dmgH(Me) in some way.…”

Section: Introductionmentioning

confidence: 88%

Hindered Rotation Leading to Nonequivalence in 2-Substituted Benzyl Cobaloximes: Structure−Property Relationship

Mandal

Gupta

2007

Organometallics

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Benzyl cobaloximes with substituents at the 2-position having varying electronic and steric properties have been synthesized and characterized. Three different dioximes (dmgH, dpgH, gH) have been used. The dmgH(Me) and Co-bound CH2 protons show nonequivalence in the 1H NMR at subzero temperatures. The nonequivalence has been rationalized in terms of restricted rotation of the Co−C and/or C−Ph bond and is attributed to weak interactions between axial and equatorial ligands. T c depends upon the nature of the 2-substituent and the dioxime. The molecular structures of 2-Me-C6H4CH2Co(dmgH)2Py, 2-naphthyl-CH2Co(dmgH)2Py, 2-Br-C6H4CH2Co(gH)2Py, and C6H5CH2Co(dpgH)2Py are reported. The activation energies of Co−C and C−Ph bond rotation are calculated from variable-temperature 1H NMR data using line-shape analysis. Also, the theoretical calculations using DFT are performed on 2-Me-C6H4CH2Co(dmgH)2Py and 2-Br-C6H4CH2Co(gH)2Py for the Co−C and C−Ph bond rotation. The conformational energy diagrams of these two molecules have been discussed.

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“…All other reagents were purchased from chemical suppliers and used as received. ClCoðdmgHÞðdpgHÞpy (dmgH 2 ¼ dimethylglyoxime, dpgH 2 ¼ diphenylglyoxime, and py ¼ pyridine) was prepared by the method of Gupta et al (32).…”

Section: Methodsmentioning

confidence: 99%

Catalytic hydrogen evolution from a covalently linked dicobaloxime

Valdez

Dempsey

Brunschwig

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

103

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A dicobaloxime in which monomeric Co(III) units are linked by an octamethylene bis(glyoxime) catalyzes the reduction of protons from p-toluenesulfonic acid as evidenced by electrocatalytic waves at −0.4 V vs. the saturated calomel electrode (SCE) in acetonitrile solutions. Rates of hydrogen evolution were determined from catalytic current peak heights (k app ¼ 1100 AE 70 M −1 s −1 ). Electrochemical experiments reveal no significant enhancement in the rate of H 2 evolution from that of a monomeric analogue: The experimental rate law is first order in catalyst and acid consistent with previous findings for similar mononuclear cobaloximes. Our work suggests that H 2 evolution likely occurs by protonation of reductively generated Co II H rather than homolysis of two Co III H units.hydrogen evolving catalysts | solar fuel E fficient catalytic reduction of protons to dihydrogen is a requirement for one half of a functional solar water splitting system (1, 2). Progress has been made recently in identifying catalysts capable of producing hydrogen from acidic media using either small molecule mimics of hydrogenase active sites or other synthetic systems (3-11).Our work has focused on difluoroboryl-bridged Co II -diglyoxime complexes that catalyze hydrogen evolution at low overpotentials (12)(13)(14)(15). With these complexes, hydrogen evolution is initiated upon reduction to Co I , which then reacts with a proton donor to form a Co III -hydride (Co III H). The Co III H intermediate can either undergo subsequent protonation to release H 2 and a Co III species that is reduced to regenerate the catalyst (heterolytic route) or react with another Co III H to eliminate H 2 by a homolytic route. Alternatively, Co III H can be reduced further to form Co II H, which can react via similar heterolytic or homolytic routes (16). Digital simulations of electrocatalytic waves performed by Hu et al. (17) indicated that the bimolecular homolytic Co III H route is the dominant pathway for hydrogen evolution. Our analysis of electron transfer rates in the catalytic cycle confirmed that the barriers to H 2 evolution associated with this pathway are more favorable than that for protonation of Co III H (17, 18). Recent work in our group examining the mechanism of hydrogen evolution from a photogenerated hydridocobaloxime suggests that hydrogen evolution via protonation of Co II H is favored under certain conditions (Co III H in low concentrations with reducing equivalents in excess) (16). Computational studies reported by 20) and Muckerman (21) suggest that Co II H protonation is a very favorable reaction pathway and that relative fluxes through the homolytic Co III H and heterolytic Co II H channels depend on experimental conditions (relative concentrations of acid and catalyst).In the low-barrier homolytic mechanism, two Co III H species must diffuse together in solution in order to react and release H 2 . It follows that immobilization onto an electrode surface would disfavor this pathway (7,22,23). It is of interest in this context that...

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Organocobaloximes with mixed dioxime equatorial ligands: a convenient one-pot synthesis. X-ray crystal structures of BnCoIII(dmgH)(dpgH)Py and BnCOIII(chgH)(dpgH)py

Cited by 20 publications

References 26 publications

Pyrazine bridged benzyl dicobaloximes: Competition between π-interaction and steric crowding in crystal structure

Pyrazine bridged benzyl dicobaloximes: Competition between π-interaction and steric crowding in crystal structure

Hindered Rotation Leading to Nonequivalence in 2-Substituted Benzyl Cobaloximes: Structure−Property Relationship

Catalytic hydrogen evolution from a covalently linked dicobaloxime

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